Differential measurements of γγ→ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at √(sNN) = 5.02 TeV with ATLAS
Abstract
This paper presents the first differential fiducial measurements of γγ→ττ using 1.93 nb−1 of Pb+Pb data at √(sNN) = 5.02 TeV recorded by the ATLAS detector. Events in which one of the τ-leptons decays into a muon and two neutrinos τ→ντν̅μμ are selected and are categorized into three regions by the presence of an electron or either one or three charged-particle track(s) from the second τ-lepton decay. The measurement is performed in events where both Pb ions remain intact and no neutrons are emitted. Differential cross-sections are measured for seven variables in three fiducial regions at particle level. The measurements are compared to theory predictions with different photon flux models and spin correlation effects. For the fiducial region with one muon and one electron in the final state, comparisons to next-to-leading-order electroweak predictions are also made. The transverse momentum (pT) of the decay muon, the pT of the visible decay particles of the other τ-lepton, the total pT, invariant mass, and pseudorapidity of the visible particles from the di-τ system, and the rapidity and acoplanarity of the visible decay particles from either τ-lepton are measured. A maximum-likelihood fit to the muon transverse-momentum distributions in the three regions before unfolding is performed to extract the τ-lepton anomalous magnetic moment aτ and electric dipole moment dτ, the latter for the first time in heavy ion collisions. The observed 95% confidence level intervals are −0.057 <aτ< 0.035 and |dτ|< 2.7 × 10−16 ecm.}
Versions
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BibTeX
@misc{collaboration2026differential,
title = {{Differential measurements of $γγ\toττ$ and constraints on $τ$-lepton electromagnetic moments in Pb+Pb collisions at $\sqrts__\textNN = 5.02$ TeV with ATLAS}},
author = {The ATLAS Collaboration},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.04584},
eprint = {2605.04584},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.04584},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Differential measurements of γγ→ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at √(s__NN) = 5.02 TeV with ATLAS
AU - The ATLAS Collaboration
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2605.04584
UR - https://arxiv.org/abs/2605.04584
AB - This paper presents the first differential fiducial measurements of γγ→ττ using 1.93 nb^−1 of Pb+Pb data at √(s__NN) = 5.02 TeV recorded by the ATLAS detector. Events in which one of the τ-leptons decays into a muon and two neutrinos τ→ν_τν̅_μμ are selected and are categorized into three regions by the presence of an electron or either one or three charged-particle track(s) from the second τ-lepton decay. The measurement is performed in events where both Pb ions remain intact and no neutrons are emitted. Differential cross-sections are measured for seven variables in three fiducial regions at particle level. The measurements are compared to theory predictions with different photon flux models and spin correlation effects. For the fiducial region with one muon and one electron in the final state, comparisons to next-to-leading-order electroweak predictions are also made. The transverse momentum (p_T) of the decay muon, the p_T of the visible decay particles of the other τ-lepton, the total p_T, invariant mass, and pseudorapidity of the visible particles from the di-τ system, and the rapidity and acoplanarity of the visible decay particles from either τ-lepton are measured. A maximum-likelihood fit to the muon transverse-momentum distributions in the three regions before unfolding is performed to extract the τ-lepton anomalous magnetic moment a_τ and electric dipole moment d_τ, the latter for the first time in heavy ion collisions. The observed 95% confidence level intervals are −0.057 <a_τ< 0.035 and |d_τ|< 2.7 × 10^−16 ecm.}
ER -